Questions and Answers
What is the Formation of Becke Line?
The Becke Line appears when a glass particle is mounted in an oil with the same refractive index.
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What does the Becke Line represent?
A visible halo of light formed around a glass particle in oil.
What happens to the Becke Line when the higher refractive index material is focused on?
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What is required to see contrast under the microscope?
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What is the purpose of Cargille Liquids in the Becke Line test?
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If the Becke Line moves into the glass, what can be inferred about the refractive index of the glass?
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What should you do after determining a rough range of the glass's refractive index?
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Study Notes
Formation of Becke Line
- Becke Line formation occurs at the interface of two materials with different refractive indices: a particle and the mounting oil.
Refraction of Light
- Light refraction occurs when passing through materials of different refractive indices, causing light to bend around object edges.
- The direction of bending depends on which material has the higher refractive index, resulting in a visible halo called the Becke Line.
Observations with Becke Line
- When focusing on glass with a higher refractive index, the Becke Line appears to move towards the glass as the stage is lowered.
- A decrease in Becke Line size indicates movement towards the particle, while in the case where oil has a higher refractive index, the Becke Line appears to move towards the oil.
Key Rule for Observing Becke Line
- The Becke Line always moves towards the material with the higher refractive index when focusing on the edge and lowering the stage.
Importance of Refraction in Imaging
- Contrast under the microscope is achieved by light passing through and being scattered by the sample, with the objective lens focusing these rays for interference.
Visibility Conditions
- When a glass particle has the same refractive index as the surrounding liquid, it appears invisible under the microscope, assuming there is no color differentiation.
Application of Becke Line Test
- The darker edge represents the glass particle, and the bright halo is the Becke Line. Observing the movement of this halo can indicate which material has a higher refractive index.
Methodology for Becke Line Testing
- Starting with known refractive index oils (Cargille Liquids), the glass is mounted, and the Becke Line test is performed.
- If the Becke Line moves towards the glass while using an oil of 1.500 R.I., it indicates the glass refractive index is greater than 1.500.
Determining Glass Refractive Index Range
- If the Becke Line moves towards an oil with a higher R.I. (1.600), the glass R.I. will be between 1.500 and 1.600, guiding further tests.
Refining the Refractive Index Measurement
- Subsequent tests with intermediate oils (e.g., 1.550 R.I.) help narrow down the exact refractive index until the glass disappears in an oil of equal refractive index.
Becke Line Method Steps
- Use medium to high power magnification during observation.
- Observe the Becke Line movement by closing the aperture diaphragm and lowering the stage to confirm the higher R.I. material.
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Description
Explore the concept of the Becke Line through these flashcards. Learn how the refractive index of a glass particle interacts with a mounting oil, affecting light refraction. This quiz is essential for understanding optical mineralogy.
